A Isometric Drawings ISOMETRIC BASICS Isometric drawings are a means of drawing an object in picture form for better clarifying the object’s appearance. These types of drawings resemble a picture of an object that is drawn in two dimensions. As a result, existing AutoCAD commands such as LINE and COPY are used for producing isometric drawings. This chapter will explain isometric basics including how regular, angular, and circular objects are drawn in isometric. Numerous isometric aids such as snap and isometric axes will be explained to assist in the construction of isometric drawings. Isometric drawings consist of two-dimensional drawings that are tilted at some angle to expose other views and give the viewer the illusion that what he or she is viewing is a three-dimensional drawing. The tilting occurs with two 30° angles that are struck from the intersection of a horizontal baseline and a vertical line (see Figure A–1). The directions formed by the 30° angles represent actual dimensions of the object; this may be either the width or depth. The vertical line in most cases represents the height dimension.
Figure A–1
Figure A–2 is a very simple example of how an object is aligned to the isometric axis. Once the horizontal baseline and vertical line are drawn, the 30° angles are projected from this common point, which becomes the reference point of the isometric view. In this example, once the 30° lines are drawn, the baseline is no longer needed and it is usually discarded through erasing. Depending on how the object is to be viewed, width and depth measurements are made along the 30° lines. Height is measured along the vertical line. Figure A–2 has the width dimension measured off to the left 1
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30° line while the depth dimension measures to the right along the right 30° line. Once the object is blocked with overall width, depth, and height, details are added, and lines are erased and trimmed, leaving the finished object. Holes in isometric drawings no longer appear as full circles but rather as ellipses. Techniques of drawing circles in isometric will be discussed later in this chapter.
Figure A–2
Notice that the objects in Figure A–3 both resemble the object in Figure A–2 except they appear from a different vantage point. The problem with isometric drawings is that if an isometric of an object is drawn from one viewing point and you want an isometric from another viewing point, an entirely different isometric drawing must be generated from scratch. Complex isometric drawings from different views can be very tedious to draw. Another interesting observation concerning the objects in Figure A–3 is that one has hidden lines while the other does not. Usually only the visible surfaces of an object are drawn in isometric, with hidden lines left out. Although this is considered the preferred practice, there are always times when hidden lines are needed to clarify very complex isometric drawings.
Figure A–3
Isometric Drawings
CREATING AN ISOMETRIC GRID Figure A–4 shows the current AutoCAD screen complete with cursor and grid on. In manual drawing and sketching days, an isometric grid was used to lay out all lines before the lines were transferred to paper or Mylar for pen and ink drawings. An isometric grid may be defined in an AutoCAD drawing through the SNAP command. This would be the same grid found on isometric grid paper.
Figure A–4
The display screen in Figure A–5 reflects the use of the SNAP command and how this command affects the current grid display: Command: SN (For SNAP) Snap spacing or ON/OFF/Aspect/Rotate/Style <0.2500>: S (for Style) Standard/Isometric
: I (for Isometric) Vertical spacing <0.5000>: (Press ENTER to accept default value)
Choosing an isometric style of snap changes the grid display from orthographic to isometric, shown in Figure A–5. The grid distance conforms to a vertical spacing height that you specify. As the grid changes, notice the display of the typical AutoCAD cursor; it conforms to an isometric axis plane and is used as an aid in constructing isometric drawings.
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Figure A–5
To see how this vertical spacing distance affects the grid, changing it to isometric, see Figure A–6. The grid dot at “A” becomes the reference point where the horizontal baseline is placed followed by the vertical line represented by the dot at “B.” At dots “A” and “B,” 30° lines are drawn; points “C” and “D” are formed where they intersect. This is how an isometric screen display is formed.
Figure A–6
ISOPLANE MODES The AutoCAD cursor has always been the vehicle for drawing objects or constructing windows for object selection mode. Once in isometric snap mode, AutoCAD supports three axes to assist in the construction of isometric drawings. The first axis is the Left axis and may control that part of an object falling into the left projection plane. The Left axis cursor displays a vertical line intersected by a 30°-angle line, which is drawn to the left. This axis is displayed in the illustration in Figure A–7 and in the following drawing:
Isometric Drawings
Figure A–7
The next isometric axis is the Top mode. Objects falling into the top projection plane may be drawn using this isometric axis. This cursor consists of two 30°-angle lines intersecting each other forming the center of the cursor. This mode is displayed in Figure A–8 and in the following drawing:
Figure A–8
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The final isometric axis is called the Right mode and is formed by the intersection of a vertical line and a 30° angle drawn off to the right. As with the previous two modes, objects that fall along the right projection plane of an isometric drawing may be drawn with this cursor. It is displayed in Figure A–9 and in the following drawing. The current Ortho mode affects all three modes. If Ortho is on, and the current isometric axis is Right, lines and other operations requiring direction will be forced to be drawn vertical or at a 30° angle to the right, as shown in the following drawing:
Figure A–9
RESETTING GRID AND SNAP TO THEIR DEFAULT VALUES Once an isometric drawing is completed, it may be necessary to change the grid, snap, and cursor back to normal. This might result from the need to place text on the drawing, and the isometric axis now confuses instead of assists in the drawing process. Use the following prompts to reset the snap back to the Standard spacing. See Figure A–10. Command: SN (For SNAP) Snap spacing or ON/OFF/Rotate/Style <0.2500>: S (for Style) Standard/Isometric : S (for Standard) Spacing/Aspect <0.5000>: (Press ENTER to accept the default value)
Notice that when you change the snap style to Standard, the AutoCAD cursor reverts to its original display.
Isometric Drawings
Figure A–10
ISOMETRIC AIDS IN THE DRAFTING SETTINGS DIALOG BOX Choosing Drafting Settings… from the Tools pull-down menu in Figure A–11A displays the Drafting Settings dialog box in Figure A–11B. Here, in addition to Snap and Grid, an Isometric area exists to automatically set up an isometric grid by clicking in the radio button next to Isometric Snap. This has the same effect as using the SNAP-Style-Isometric option.
Figure A–11A
Figure A–11B
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Various methods exist to switch from one isometric axis mode to another. By default, after you set up an isometric grid, the Left isometric axis mode is active (see Figure A–12). When you press CTRL+E, the Left axis mode changes to the Top axis mode. Pressing CTRL+E again changes from the Top axis mode to the Right axis mode. Pressing CTRL+E a third time changes from the Right axis mode back to the Left axis mode, and the pattern repeats from here. Using this keyboard entry, it is possible to switch or toggle from one mode to another. The F5 function key also allows you to scroll through the different Isoplane modes.
Figure A–12
CREATING ISOMETRIC CIRCLES Circles appear as ellipses when drawn in any of the three isometric axes. The ELLIPSE command has a special Isocircle option to assist in drawing isometric circles; the Isocircle option will appear in the ELLIPSE command only if the current SNAP-Style is Isometric (see Figure A–13). The prompt sequence for this command is: Command: EL (For ELLIPSE) Arc/Center/Isocircle/: I (for Isocircle) Center of circle: (Select a center point) /Diameter: (Enter a value for the radius or type “D” for diameter and enter a value)
When you draw isometric circles using the ELLIPSE command, it is important to match the isometric axis with the isometric plane the circle is to be drawn in. Figure A–14 shows a cube displaying all three axes. Try It! - Open the drawing file A_Iso Ellipse1. This drawing is similar to Figure A–14. Using the three isometric planes, construct ellipses with a diameter of 2.00 units using the “X” points as centers.
Isometric Drawings
Figure A–13
Figure A–14
Figure A–15 shows the result of drawing an isometric circle using the wrong isometric axis. The isometric box is drawn in the Top isometric plane while the current isometric axis mode is Left. An isometric circle can be drawn to the correct size, but notice that it does not match the box it was designed for. If you notice halfway through the ELLIPSE command that you are in the wrong isometric axis, press CTRL+E until the correct axis appears.
Figure A–15
BASIC ISOMETRIC CONSTRUCTION Any isometric drawing, no matter how simple or complex, has an overall width, height, and depth dimension. Start laying out the drawing with these three dimensions to create an isometric box illustrated in the example in Figure A–16A. Some techniques rely on piecing the isometric drawing together by views; unfortunately, it is very easy to get lost in all of the lines using this method. Once a box is created from overall dimensions, somewhere inside the box is the object. With the box as a guide, begin laying out all visible features in the primary planes. Use the Left, Top, or Right isometric axis modes to assist you in this construction process. See Figure A–16B.
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Figure A–16A
Figure A–16B
You may use existing AutoCAD editing commands, especially COPY, to duplicate geometry to show depth of features, as shown in Figure A–16C. The OFFSET command should not be attempted for performing isometric drawings. Next, use the TRIM command to partially delete geometry where objects are not visible. Remember, most isometric objects do not require hidden lines. Use the LINE command to connect intersections of surface corners. The resulting isometric drawing is illustrated in Figure A–16D.
Figure A–16C
Figure A–16D
Try It! - Open the drawing file A_Iso Basic in Figure A–16B. Continue copying and trimming line segments until you achieve the desired results in Figure A–16D. CREATING ANGLES IN ISOMETRIC—METHOD #1 Drawing angles in isometric is a little tricky but not impossible. The two-view drawing in Figure A–17 has an angle of unknown size; however, one endpoint of the angle measures 2.06 units from the top horizontal line of the Front view at “B,” and the
Isometric Drawings
other endpoint measures 1.00 unit from the vertical line of the Front view at “A.” This is more than enough information to lay out the endpoints of the angle in isometric. You can use the MEASURE command to lay out these distances easily. The LINE command is then used to connect the points to form the angle.
Figure A–17
Before using the MEASURE command, set the PDMODE variable to a new value of 3. Points will appear as an X instead of a dot, as shown in Figure A–18A. Points may also be set through the Point Style dialog box found in the Format menu. Now use the MEASURE command to set off the two distances. Command: PDMODE New value for PDMODE <0>: 3 Command: ME (For MEASURE) Select object to measure: (Select the inclined line at “A”) /Block: 1.00 Command: ME (For MEASURE) Select object to measure: (Select the vertical line at “B”) /Block: 2.06
When using the MEASURE command, the measuring will occur at the nearest endpoint of the line where the line was selected. Once the points have been placed, the LINE command is used to draw a line from one point to the other using the OSNAP-Node option (see Figure A–18B).
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Figure A–18A
Figure A–18B
Try It! - Open the drawing file A_Iso Angle1. Use the previous figures as guides in constructing the angle in isometric mode in Figure A–18B. Notice that you may get more points than needed. Draw the line from the nodes nearest the end of the line you selected with the MEASURE command. CREATING ANGLES IN ISOMETRIC—METHOD #2 The same two-view drawing is illustrated in Figure A–19. This time, one distance is specified along with an angle of 30°. Even with the angle given, the position of the isometric axes makes any angle construction by degrees inaccurate. The distance XY is still needed for constructing the angle in isometric. Use the MEASURE command to find distance XY, place a point, and connect the first distance with the second to form the 30° angle in isometric. It is always best to set the PDMODE system variable to a new value in order to visibly view the point. Points may also be set through the Point Style dialog box found in the Format menu. A new value of 3 will assign the point as an X.
Figure A–19
Isometric Drawings
See Figures 16–20A, 16–20B, and the following prompt sequences to change the point mode and measure the appropriate distances in the previous step. Command: PDMODE New value for PDMODE <0>: 3 Command: ME (For MEASURE) Select object to measure: (Select the inclined line at “A” in Figure A–20A) /Block: 1.00 Command: ME (For MEASURE) Select object to measure: (Select the vertical line at “B” in Figure A–20A) /Block: End of (Select the endpoint of the line at X in the 2-view drawing in Figure A–19) Second point: Int of (Select the intersection at Y in the 2-view drawing in Figure A–19)
Line “B” is selected as the object to measure (see Figure A–20A). Since this distance is unknown, the MEASURE command may be used to set off the distance XY by identifying an endpoint and intersection from the Front view in Figure A–19. This means the view must be constructed only enough to lay out the angle and project the results to the isometric using the MEASURE command and the preceding prompts. The result is illustrated in Figure A–20B.
Figure A–20A
Figure A–20B
Try It! - Open the drawing file A_Iso Angle2. Use the previous figures as guides in constructing the angle in isometric mode in Figure A–20B. You can check the accuracy of your construction by comparing distances using the DISTANCE command on the Front view of the two-view drawing and on the same line in the Isometric. The values should be the same. ISOMETRIC CONSTRUCTION USING ELLIPSES Constructing circles as part of isometric drawing is possible using one of the three isometric axis positions. It is up to you to decide which axis to use. Before this, how-
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ever, an isometric box consisting of overall distances is first constructed, as shown in Figure A–21A. Use the ELLIPSE command to place the isometric circle at the base. To select the correct axis, press CTRL+E or F5 until the proper axis appears in the form of the cursor. Place the ellipses. Lay out any other distances. For ellipses at different positions, press CTRL+E or F5 to select another isometric axis (see Figure A–21B).
Figure A–21A
Figure A–21B
Use the TRIM command to trim away any excess objects that are considered unnecessary, as shown in Figure A–21C. Use the LINE command to connect endpoints of edges that form surfaces and from tangents of arcs to tangents of arcs on paralell planes, as shown in Figure A–21D.
Figure A–21C
Figure A–21D
Try It! - Open the drawing file A_Iso Ellipse2. Complete the isometric drawing until your image is similar to Figure A-21D. CREATING ISOMETRIC SECTIONS In some cases, it is necessary to cut an isometric drawing to expose internal features. The result is an isometric section similar to a section view formed from an orthographic drawing. The isometric section differs, however, because the cutting plane is usually along one of the three isometric axes. Figure A–22A displays an orthographic section in addition to the isometric drawing. The isometric in Figure A–22B has additional lines representing surfaces cut by the cutting plane line. The lines to define these surfaces are formed through the LINE command
Isometric Drawings
in addition to a combination of Top and Right isometric axis modes. During this process, Ortho mode is toggled on and off numerous times depending on the axis direction. Use the TRIM command to remove objects from the half that will eventually be discarded.
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Figure A–22A
Once ellipses are trimmed, the remaining objects representing the front half of the isometric are removed, exposing the back half. The front half is then discarded. This has the same effect as conventional section views where the direction of sight dictates which half to keep. For a full section, the BHATCH command with the angle set at 15 degrees is used to draw section lines on the surfaces being cut by the cutting plane line, as in Figure A–22C. Surfaces designated holes or slots not cut are not crosshatched. This same procedure is followed for converting an object to a half section.
Figure A–22B
Figure A–22C
Try It! - Open the drawing file A_Iso Section. Use the previous figures as guides in constructing the isometric section in Figure A–22C. EXPLODED ISOMETRIC VIEWS Isometric drawings are sometimes grouped together to form an exploded drawing showing how a potential or existing product is assembled (see Figure A–23). This involves aligning parts that fit with line segments, usually in the form of centerlines. Bubbles identifying the part number are attached to the drawing. Exploded isometric drawings
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come in handy for creating bill of material information and, for this purpose, they have an important application to manufacturing. Once the part information is identified in the drawing and title block area, this information is extracted and brought into a third-party business package where important data collection information is used to actually track the status of parts in production in addition to the shipping date for all finished products.
Figure A–23
ISOMETRIC ASSEMBLIES Assembly drawings show the completed part as if it were to be assembled (see Figure A–24). Sometimes this drawing has an identifying number placed with a bubble for bill of material needs. Assembly drawings are commonly placed on the same display screen as the working drawing. With the assembly alongside the working drawing, you have a pictorial representation of what the final product will look like, and this can help you to understand the orthographic views.
Figure A–24
Isometric Drawings
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TUTORIAL EXERCISE: PLATE.DWG
Purpose
Layers
The purpose of this tutorial exercise is to use a series of coordinates along with AutoCAD editing commands to construct an isometric drawing of the plate in Figure A–25.
Create a layer called “Object” and assign this layer the color Green.
System Settings Begin a new drawing called “Plate.” Use the Drawing Units dialog box to change the number of decimal places past the zero from four to two. Keep the remaining default unit values. Using the LIMITS command, keep (0,0) for the lower left corner and change the upper right corner from (12.00,9.00) to (10.50,8.00). Perform a ZOOM-ALL after changing limits. Use the GRID command and change the grid spacing from 0.50 to 0.25 units. Do not turn the Snap or Ortho modes on. Check to see that the following Object Snap modes are already set: Endpoint, Extension, Intersection, and Center.
Suggested Commands Begin this exercise by changing the grid from the standard display to an isometric display using the SNAP-Style option. Use absolute and polar coordinates to lay out the base of the plate. Then begin using the COPY command followed by TRIM to duplicate objects and clean up or trim unnecessary geometry. Whenever possible, substitute the appropriate command alias in place of the full AutoCAD command in each tutorial step. For example, use “CP” for the COPY command, “L” for the LINE command, and so on. The complete listing of all command aliases is located in Chapter 1, Table 1–2.
tutorial E X E R C I S E
Figure A–25
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STEP 1
Set a new polar tracking angle of 30° through the Polar Tracking tab of the Drafting Settings dialog box in Figure A– 26A. Make the Object layer current. Then use the LINE command to draw the object in Figure A–26B. Notice, in the prompt sequence, that the Direct Distance mode is used because of the polar tracking angle setting of 30°. Also, be sure to turn Polar mode on by clicking on the POLAR button in the status bar. Command: L (For LINE) Specify first point: 5.50,0.75
Specify next point or [Undo]: (Move your cursor up and to the right until the polar angle tooltip reads 30 degrees and enter 3.25) Specify next point or [Undo]: (Move your cursor up and to the left until the polar angle tooltip reads 150 degrees and enter 5.00) Specify next point or [Close/Undo]: (Move your cursor down and to the left until the polar angle tooltip reads 210 degrees and enter 3.25) Specify next point or [Close/Undo]: C (To close the shape and exit the command)
Figure A–26A
Figure A–26B
Isometric Drawings
STEP 2
Copy the four lines drawn in Step 1 up a distance of 2.50 units in the 90° direction in Figure A–27. Command: CP (For COPY) Select objects: (Select lines “A”, “B”,”C”, and “D”) Select objects: (Press ENTER to continue) Specify base point or displacement, or [Multiple]: (Pick the endpoint of the line at “A”) Specify second point of displacement or 
